The invention is generally related to ultrasonic liquid gauging systems. More particularly, the invention is related to improving the detection of valid echoes under low liquid level and echo drop out conditions to thereby improve the accuracy of the measured liquid quantity.
Ultrasonic liquid gauging systems are well known in the art, and have been used, for example, in aircraft fuel gauging systems. Such systems typically operate based on echo ranging, by which the elapsed time between the transmission of ultrasonic energy from an ultrasonic transducer and the detection of ultrasonic echoes can be used to determine the distance of the reflecting surface to the ultrasonic transducer. Such reflections occur at boundaries that define impedance mismatches between the liquid and another surface or object. A velocity of sound (VOS) target can be used that is positioned a predetermined distance from the transducer to provide a reference value for the VOS through the liquid to improve the accuracy of the calculated distances of the liquid surface from the transducer.
For low liquid levels, a particular problem that can arise is the detection of secondary and tertiary echoes from multiple or harmonic reflections at the liquid surface of the transmitted ultrasonic energy. Echoes can also be lost or missed, including echoes from the surface as well as from the target.
The objectives exist, therefore, to provide improved processing of echo data in ultrasonic liquid gauging systems.